U.S. patent number 4,699,150 [Application Number 06/864,563] was granted by the patent office on 1987-10-13 for ultrasonic transducer assembly for medical diagnostic examinations.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Akira Fukumoto, Masami Kawabuchi, Koji Matsuo, Fumio Muramatsu, Koetsu Saito.
United States Patent |
4,699,150 |
Kawabuchi , et al. |
October 13, 1987 |
Ultrasonic transducer assembly for medical diagnostic
examinations
Abstract
An ultrasonic transducer for medical diagnostic examinations
which comprises a transducer element having one surface through
ultrasonic waves are emitted, an acoustic impedance matcher, and a
contact member brought to contact with an object being examined and
formed on the one surface of the ultrasonic transducer element. The
contact member includes at least a flat plate or an acoustic lens
made of a-4-methylpentene-1-base polymer which has high mechanical
strength. Transducer arrays and assemblies using such polymer as a
member directly contacted with human body are also described.
Inventors: |
Kawabuchi; Masami (Yokohama,
JP), Matsuo; Koji (Tokyo, JP), Muramatsu;
Fumio (Atsugi, JP), Fukumoto; Akira (Tokyo,
JP), Saito; Koetsu (Sagamihara, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (JP)
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Family
ID: |
14316208 |
Appl.
No.: |
06/864,563 |
Filed: |
May 16, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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618367 |
Jun 7, 1984 |
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Foreign Application Priority Data
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Jun 7, 1983 [JP] |
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58-102025 |
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Current U.S.
Class: |
600/446; 600/472;
73/644 |
Current CPC
Class: |
G10K
11/30 (20130101); G10K 11/02 (20130101) |
Current International
Class: |
G10K
11/02 (20060101); G10K 11/00 (20060101); G10K
11/30 (20060101); A61B 010/00 () |
Field of
Search: |
;128/660-663 ;73/632,644
;310/335 ;524/413 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Howell; Kyle L.
Assistant Examiner: Smith; Ruth S.
Attorney, Agent or Firm: Lowe, Price, LeBlanc, Becker &
Shur
Parent Case Text
This application is a continuation of application Ser. No. 618,367,
filed June 7, 1984, now abandoned.
Claims
What is claimed is:
1. An ultrasonic transducer assembly for use in medical diagnostic
examinations comprising (a) an ultrasonic transducer member having
(i) a transducer element with one surface through which an
ultrasonic wave is emitted, (ii) an acoustic impedance matcher
formed on the one surface, and (iii) an acoustic lens formed on
said acoustic impedance matcher, (b) means for rotationally moving
said ultrasonic transducer member, (c) a casing having an acoustic
window of a semi-circular form in section and a uniform thickness
and encasing said ultrasonic transducer member therein, and (d) an
acoustic wave transfer liquid filling said casing, said acoustic
window being adapted to contact an object being examined and
consisting of a 4-methylpentene-1-base polymer selected from the
group consisting of methylpentene homopolymer and copolymers of
4-methylpentene-1 with an olefinic manner, wherein said polymer has
an initial flexural modulus of 7,500 to 24,000 kg/cm.sup.2, a
Charpy impact strength of 4 to 5 kg.cm/cm.sup.2, an Izod impact
strength of 10 to 50 kg.cm/cm, a Shore hardness of 100, and a
Rockwell hardness of 60 to 90.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to ultrasonic transducers for use in
ultrasonic diagnostic systems and more particularly, to the use of
a specific type of polymer material for reinforcement of the
transducer.
2. Description of the Prior Art
In the medical fields, ultrasonic diagnostic systems have been
widely used in recent years. The ultrasonic diagnostic systems make
use of a variety of ultrasonic transducers. Typical ultrasonic
transducers are illustraed with reference to FIGS. 1(a) through
1(c) in which they are schematically shown.
Ultrasonic transducers shown in FIGS. 1(a) and 1(b) are of the
single element type. In the figures, reference numerals 1, 2
indicate electrodes attached to a piezoelectric ceramic material 3
on opposite sides thereof, thereby giving a transducer element 4.
The electrodes 1 and 2 have lead wires 5 and 6, respectively. On
the electrode 2 is formed an acoustic impedance matcher 7 made of
one or more layers. This matcher 7 serves to transmit an ultrasonic
wave generated from the transducer element 4 in order to improve
energy transfer between the high impedance piezoelectric ceramic
material and the low impedance of human body being examined as is
known in the art. The matcher 7 has an acoustic lens 8 on the side
opposite to the electrode 2, by which the ultrasonic wave
propagated through the acoustic impedance matcher 7 is focused and
transmitted to the object being examined with an improved lateral
resolution. In FIG. 1(a), a damping member 11 is provided in order
to mechanically damp the transducer element 4 therewith.
FIG. 1(c) shows a linear transducer array. In this array, a
multiplicity of transducer elements, e.g. several tens to several
hundreds of elements, are linearly arranged on a plane.
The ultrasonic transducers having such constructions as described
above are brought to contact with an object being examined at one
surface of the acoustic lens 8 so as to transmit and receive
ultrasonic waves, thereby diagnostically examining the object.
The acoustic impedance matcher 7 of the known ultrasonic
transducers is usually constituted of one layer of a mixture of
metal powder and a resin, or two layers including a first layer of
glass and a second layer of plastic resin, with a thickness of as
small as 0.2 to 0.5 mm. The acoustic lens 8 is made, for example,
of silicone rubber and has a thickness as small as 0.5 to 1 mm. One
of disadvantages of the known transducers is that they are low in
mechanical strength as a whole and especially, the portion which is
brought to direct contact with an object being examined is low in
mechanical strength. Although the ultrasonic transducer having the
construction shown in FIG. 1(a) is improved in mechanical strength
over those transducers of FIGS. 1(b) and 1(c), it has the drawback
that its sensitivity lowers by 4 to 10 dB.
In certain transducers having constructions similar to those shown
in FIGS. 1(a) through 1(c), a protective rubber or resin film is
further provided on the side of the acoustic lens 8 which is
directly contacted with an object being examined, or between the
acoustic lens 8 and the acoustic impedance matcher 7. However, the
rubber or resin materials are not favorable from the standpoint of
acoustic characteristics: an acoustic impedance thereof is not
suitable, acoustic waves attenuate considerably, and/or sensitivity
and ring down characteristic lower considerably.
On the other hand, there is known a mechanical scanner-type
ultrasonic transducer assembly which comprises an ultrasonic
transducer of the construction of FIG. 1(a) or 1(b) encased in a
container having an acoustic window. In the container is filled a
nearby fluid such as degassed water. In operation, the ultrasonic
transducer is mechanically swung so that an object being examined
is sector scanned. In this case, the acoustic window which is
directly contacted with the object is one of the most important
parts of the assembly. The acoustic window must have an acoustic
impedance similar to or near the acoustic impedance of the human
body (i.e. 1.5 to 1.7.times.10.sup.5 g/cm.sup.2 S) and a reduced
degree of acoustic wave attenuation with high mechanical strength.
This window is usually made of polyethylene which has an acoustic
impedance of 2.3.times.10.sup.5 g/cm.sup.2 S and an acoustic wave
attenuation as large as about 1 dB/mm/MHz. The mechanical hardness
is as low as about 90 as expressed by Shore hardness A. Thus, the
acoustic characteristics and mechanical reliability are not
necessarily satisfactory.
SUMMARY OF THE INVENTION
It is an object of the invention to provide ultrasonic transducer
assemblies which include a member made of a specific type of
polymer material.
According to one embodiment of the invention, an ultrasonic
transducer comprises a transducer element having one surface
through which ultrasonic waves are emitted, an acoustic impedance
matcher having a thickness of a quarter wavelength formed on the
one surface of the transducer element, and a contact member which
is brought to contact with an object being examined and formed on
the one surface of the ultrasonic transducer element, the contact
member being made of a 4-methylpenten-1-base polymer of high
mechanical strength. The contact member may be in the form of a
thin flat plate by which a transducer of the non-focussing type is
obtained. On the other hand, the contact member may be in the form
of a plano-concave form. By this, the transducer obtained is of the
focussing type. In the latter case, the contact member serves also
as an acoustic lens. Alternatively, the contact member may be
constituted of an integral combination of an acoustic lens made of
silicone rubber and a reinforcement of a 4-methylpentene-1-base
polymer. The acoustic lens and the reinforcement may be formed on
the matcher in this or reversed order.
According to another embodiment of the invention, a transducer
array is also provided in which a multiplicity of transducer
elements are arranged on a flat or spherically curved surface so
that they are acoustically separated from one another. On the flat
or spherically curved surface are formed an acoustic impedance
matcher and a contact member in the same manner as described with
reference to the first embodiment.
A further embodiment of the invention comprises a container having
an acoustic window made of 4-methylpentene-1-base polymer through
which an ultrasound wave generated from an ultrasonic transducer is
transmitted and received. An acoustic wave transfer medium such as
degassed water is filled in the container. The acoustic window is
contacted with an object being examined.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) through 1(c) are schematic sectional views of known
ultrasonic transducers, respectively;
FIGS. 2(a) through 2(f) are schematic sectional views showing
ultrasonic transducers of the single element types according to one
embodiment of the invention;
FIGS. 3(a) and 3(b) are schematic sectional views showing linear or
curved array transducers according to another embodiment of the
invention;
FIG. 4 is a graphic representation of the relation between acoustic
wave attenuation and frequency of polymethylpentene;
FIG. 5 is a schematic sectional view of an ultrasonic transducer
assembly of the mechanical scan type according to a further
embodiment of the invention; and
FIG. 6 is a schematic sectional view of an ultrasonic transducer
assembly having an acoustic wave coupler according to the
invention.
DETAILED DESCRIPTION AND EMBODIMENTS OF THE INVENTION
Reference is now made to the accompanying drawings, in which like
reference numerals indicate like parts, and particularly to FIGS.
2(a) through 2(f). FIGS. 2(a) through 2(f) show single element
types of ultrasonic transducers according to the invention. In FIG.
2(a), there is shown transducer 10 of a non-focussing type which
includes, similar to FIGS. 1(a) through 1(c), electrodes 11, 12
having lead wires 15, 16, respectively, and a piezoelectric ceramic
material 13 interposed between the electrodes 11, 12, thereby
giving a transducer element 14. On the electrode 12 are formed an
acoustic impedance matcher 17 and a contact member 18. The contact
member 18 is brought to direct contact with an object being
examined (not shown), e.g. a human body. The acoustic impedance
matcher 17 is made of glass, synthetic resins and the like as is
well known in the art and may be constituted of a single layer or
two or more layers. The thickness of the matcher 17 is an about
quarter wavelength of an acoustic wave passing through the acoustic
impedance matcher 17 as usual.
The contact member 18 is made of 4-methylpentene-1-base polymer and
has generally a thickness of from 1 to 5 mm. The
4-methylpentene-1-base polymer is a kind of a polyolefin.
4-Methylpentene-1 is a dimer of propylene. The term
`4-methylpentene-1-base polymer` means methylpentene homopolymer,
or copolymers of 4-methylpentene-1 with olefinic monomers such as
ethylene, propylene, butylene and higher olefins, and will be
hereinafter referred to simply as polymethylpentene. The
methylpentene homopolymer has recurring units of the formula
##STR1## The polymethylpentene is prepared according to known
techniques for ordinary olefins and is commercially available, for
example, from Mitsui Petrochemical Industries, Limited under the
designations of RT 18, DX 810, MX 004 and MX 221M. Such a polymer
usually has an acoustic impedance ranging from 1.46 to
1.70.times.10.sup.5 g/cm.sup.2.S at temperatures of from 25.degree.
to 37.degree. C., which is thus very close or equal to an acoustic
impedance of the human body of 1.54.times.10.sup.5 g/cm.sup.2.S.
The polymethylpentene has the following physical characteristics:
initial flexural modulus of 7,500 to 24,000 kg/cm.sup.2, Charpy
impact strength of 4 to 5 kg.cm/cm.sup.2, Izod impact strength of
10 to 50 kg.cm/cm, Shore hardness of 100, and Rockwell hardness of
60 to 90.
In the above embodiment, the contact member 18 is illustrated as
flat on both surfaces thereof. However, the contact member 18 may
have a plano-concave form as particularly shown in FIG. 2(b). This
arrangement makes use of a polymethylpentene acoustic lens serving
also as a reinforcement. The reason why the lens is in the
plano-concave form is that polymethylpentene which has a sound
velocity of 2000 m/second has to be shaped in plano-concave form in
order that ultrasound waves are suitably focussed in a human body
being examined. In general, the shape of an acoustic lens depends
on the ratio of a sound velocity in an acoustic lens to a sound
velocity in human body. Silicone rubber ordinarily used as an
acoustic lens has a sound velocity of about 1000 m/second and thus
should be shaped in plano-convex or biconvex form.
The contact member made of poymethylpentene is described above.
Alternatively, the contact member 18 may be made of a combination
of a reinforcement 18a and an acoustic lens 18b as shown in FIGS.
2(c) and 2(d). In this case, the acoustic lens 18b is made of
silicone rubber and has a plano-convex form. The reinforcement 18a
is made of the polymethylpentene which is high in mechanical
strength.
The transducers of the single element type may further include a
damping member 19 as particularly shown in FIG. 2(d). The damping
member 19 is usually made of synthetic resins dispersing therein
metal powder such as tungsten, ferrites or the like.
In FIGS. 2(c) and 2(d), the acoustic lens 18b is depicted as a
plano-convex lens but may have, as shown in FIG. 2(e), a biconvex
form 18b' in which case the reinforcement 18a' is in a
plano-concave form to permit integral combination with the biconvex
lens.
In order to further improve the surface strength of transducer, it
is preferably to form, on the acoustic impedance matcher 17, an
acoustic lens 18b' and a reinforcement 18a' in this order as shown
in FIG. 2(f). More particularly, the contact member 18 is made of
the plano-convex lens 18b' formed on the acoustic impedance matcher
17. The reinforcement 18a' of the plano-convex form is further
formed to fully cover the plano-convex lens 18b' therewith. In this
connection, the plane or flat surface of the lens 18b' may be
curved depending on an intended ratio of the total of a sound
velocity in the acoustic lens 18b' and a sound velocity in the
reinforcement 18a' to a sound velocity in an object being examined.
The contact member arrangement of FIG. 2(f) in which the
reinforcement 18a' is formed as the outermost layer, the transducer
is noticeably improved in impact strength, wear resistance, scratch
resistance and the like, with acoustic characteristics not
lowering.
FIG. 3(a) shows a linear array transducer 10 including a
multiplicity of transducer elements 14 which are acoustically
separated from one another and are arranged linearly. On a common
electrode 12' are formed the acoustic impedance matcher 17 and the
contact member 18. The contact member 18 is depicted as a
combination of the reinforcement 18a and the acoustic lens 18b, but
may have such arrangements as illustrated with reference to FIGS.
2(a), 2(b), 2(e) and 2(f). The multiplicity of transducer elements
14 may be arranged on a spherically curved common electrode 12 in
such a way that axes of the individual transducer elements are
extended outwardly and radially of the spherically curved surface.
This is particularly shown in FIG. 3(b).
When, for instance, acoustic transducers or arrays thereof are so
constructed as shown in FIGS. 2(a) through 2(f) and 3(a) and 3(b)
are subjected to the falling ball impact test in which a steel ball
of 5 g in weight is dropped on the contact member 18, it will be
seen that impact strength is at least 100 times as high as the
impact strength of the known acoustic transducers shown in FIGS.
1(a) through 1(c).
The transducers using the polymethylpentene member are notl so
changed with respect to the attenuation of ultrasonic wave: an
attenuation only by 0.27 dB per unit thickness by mm occurs at a
frequency of 3.5 MHz.
The dependence of the ultrasonic wave attenuation on the frequency
is very small. For instance, upon comparing with an acoustic
transducer using a silicone rubber reinforcing plate, the
transducer of the invention in which polymethylpentene is used as
the contact member is smaller in frequency dependence of the
acoustic wave attenuation with a smaller absolute value. This is
particularly shown in FIG. 4 in which line A is for silicone rubber
and line B is for polymethylpentene.
In the foregoing embodiments, polymethylpentene is used in direct
association with the acoustic impedance matcher. This polymer which
has excellent acoustic and mechanical properties may be effectively
used as a contact member which is provided at a distance from a
transducer.
One such ultrasonic transducer assembly A is shown in FIG. 5 in
which reference numeral 20 designates an ultrasonic transducer of,
for example, the known type shown in FIGS. 1(a) and 1(b). This
transducer 20 is encased in a container 21 which includes a casing
22 and an acoustic window 23 of the semi-circular form. In the
container 21 is filled a nearby or acoustic wave transfer medium 24
such as degassed water. The ultrasonic transducer 20 in the
container 21 is so arranged that it is mechanically swung by means
of a shaft 25 rotated by a motor (not shown) in directions
indicated by arrows by which ultrasonic waves 26 are transmitted
toward and received from an object or human body being examined 27
by a sector scan technique. The acoustic window 23 serving as a
contact member is made of polymethylpentene. In prior art sector
scan-type transducer assemblies, it is usual to use polyethylene as
the acoustic window. Polymethylpentene has an acoustic impedance
very close or equal to the nearby fluid 24 and the object 27. As
compared with the acoustic polyethylene window, the acoustic window
of the polymer of the invention is more reduced in multipath
reflection between the ultrasonic transduer 20 and the acoustic
window 23 and also in acoustic wave attenuation in the acoustic
window 23. Because of the high mechanical strength, even when the
window 23 is pressed against the object 27, its degree of
deformation is very small.
Although FIG. 5 shows the mechanical sector scan-type ultrasonic
transducer assembly in which the single element type ultrasonic
transducer is swung in opposite directions at high speed,
polymethylpentene polymer may be also applied as an acoustic window
of a mechanical linear scan-type ultrasonic transducer assembly.
This type of assembly has a construction similar to the
construction of FIG. 5 but in which the transducer is secured to a
moving means and is mechanically moved in opposite directions along
a strain or curved path by a pulse motor or DC motor.
FIG. 6 shows a further embodiment in which an ultrasonic transducer
assembly A different from the construction of the assembly of FIG.
5 is shown. The single element type ultrasonic transducer 20 is
detachably combined with an acoustic wave coupler 28 as shown. The
coupler 28 is constituted of a casing 29 and an acoustic window 23
of a flat plate form. On the inner side walls of the casing 29 is
lined an acoustic wave absorber 30 made of rubber having a
multiplicity of fins 31. An acoustic wave transfer fluid 24 is
filled in the casing 29. The acoustic window 23 is made of
polymethylpentene. If necessary, the casing 29 may be also made of
polymethylpentene but is usually made of other polyolefins.
In operation, acoustic waves generated from the transducer 20 are
passed through the fluid 24 and the acoustic window 23 to the
object 27 being examined. A distance between the transducer 20 and
the object 27 is suitably controlled by controlling a length, L, of
the coupler 28 by which the ultrasonic beam can be focussed to a
desired position of the object 27. The acoustic window 23 serves as
a contact member and is brought to contact with the object. The
window 23 is made of polymethylpentene, so that the assembly is
much improved in mechanical strength without a loss of acoustic
characteristics.
* * * * *